Provided by: erlang-manpages_25.2.3+dfsg-1_all bug

NAME

       win32reg - Provides access to the registry on Windows.

DESCRIPTION

       This module provides read and write access to the registry on Windows. It is essentially a
       port driver wrapped around the Win32 API calls for accessing the registry.

       The registry is a hierarchical  database,  used  to  store  various  system  and  software
       information  in  Windows.  It contains installation data, and is updated by installers and
       system programs. The Erlang installer updates the registry  by  adding  data  that  Erlang
       needs.

       The  registry  contains  keys  and values. Keys are like the directories in a file system,
       they form a hierarchy. Values are like files, they have a name and a  value,  and  also  a
       type.

       Paths  to  keys  are  left to right, with subkeys to the right and backslash between keys.
       (Remember that backslashes must be doubled in Erlang strings.) Case is preserved  but  not
       significant.

       For  example,  "\\hkey_local_machine\\software\\Ericsson\\Erlang\\5.0"  is the key for the
       installation data for the latest Erlang release.

       There are six  entry  points  in  the  Windows  registry,  top-level  keys.  They  can  be
       abbreviated in this module as follows:

       Abbreviation     Registry key
       ============     ============
       hkcr             HKEY_CLASSES_ROOT
       current_user     HKEY_CURRENT_USER
       hkcu             HKEY_CURRENT_USER
       local_machine    HKEY_LOCAL_MACHINE
       hklm             HKEY_LOCAL_MACHINE
       users            HKEY_USERS
       hku              HKEY_USERS
       current_config   HKEY_CURRENT_CONFIG
       hkcc             HKEY_CURRENT_CONFIG
       dyn_data         HKEY_DYN_DATA
       hkdd             HKEY_DYN_DATA

       The key above can be written as "\\hklm\\software\\ericsson\\erlang\\5.0".

       This module uses a current key. It works much like the current directory. From the current
       key, values can be fetched, subkeys can be listed, and so on.

       Under a key, any number of named values can be stored. They have names, types, and data.

       win32reg supports storing of the following types:

         * REG_DWORD, which is an integer

         * REG_SZ, which is a string

         * REG_BINARY, which is a binary

       Other types can be read, and are returned as binaries.

       There is also a "default" value, which has the empty  string  as  name.  It  is  read  and
       written with the atom default instead of the name.

       Some  registry  values are stored as strings with references to environment variables, for
       example, %SystemRoot%Windows. SystemRoot is an environment variable, and is to be replaced
       with  its value. Function expand/1 is provided so that environment variables surrounded by
       % can be expanded to their values.

       For more  information  on  the  Windows  registry,  see  consult  the  Win32  Programmer's
       Reference.

DATA TYPES

       reg_handle()

              As returned by open/1.

       name() = string() | default

       value() = string() | integer() | binary()

EXPORTS

       change_key(RegHandle, Key) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Key = string()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Changes  the current key to another key. Works like cd. The key can be specified as
              a relative path or as an absolute path, starting with \.

       change_key_create(RegHandle, Key) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Key = string()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Creates a key, or just changes to  it,  if  it  is  already  there.  Works  like  a
              combination of mkdir and cd. Calls the Win32 API function RegCreateKeyEx().

              The registry must have been opened in write mode.

       close(RegHandle) -> ok

              Types:

                 RegHandle = reg_handle()

              Closes the registry. After that, the RegHandle cannot be used.

       current_key(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = {ok, string()}

              Returns the path to the current key. This is the equivalent of pwd.

              Notice  that  the  current  key  is  stored  in the driver, and can be invalid (for
              example, if the key has been removed).

       delete_key(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Deletes  the  current  key,  if  it  is  valid.  Calls  the  Win32   API   function
              RegDeleteKey().  Notice  that  this  call  does  not change the current key (unlike
              change_key_create/2). This means that after the call, the current key is invalid.

       delete_value(RegHandle, Name) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Name = name()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Deletes a named value on the current key. The atom default is used for the  default
              value.

              The registry must have been opened in write mode.

       expand(String) -> ExpandedString

              Types:

                 String = ExpandedString = string()

              Expands  a  string  containing  environment  variables  between percent characters.
              Anything between two % is taken for an environment variable, and is replaced by the
              value. Two consecutive % are replaced by one %.

              A variable name that is not in the environment results in an error.

       format_error(ErrorId) -> ErrorString

              Types:

                 ErrorId = atom()
                 ErrorString = string()

              Converts a POSIX error code to a string (by calling erl_posix_msg:message/1).

       open(OpenModeList) -> ReturnValue

              Types:

                 OpenModeList = [OpenMode]
                 OpenMode = read | write
                 ReturnValue = {ok, RegHandle} | {error, ErrorId :: enotsup}
                 RegHandle = reg_handle()

              Opens   the  registry  for  reading  or  writing.  The  current  key  is  the  root
              (HKEY_CLASSES_ROOT). Flag read in the mode list can be omitted.

              Use change_key/2 with an absolute path after open.

       set_value(RegHandle, Name, Value) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Name = name()
                 Value = value()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Sets the  named  (or  default)  value  to  value.  Calls  the  Win32  API  function
              RegSetValueEx().  The  value  can be of three types, and the corresponding registry
              type is used. The supported types are the following:

                * REG_DWORD for integers

                * REG_SZ for strings

                * REG_BINARY for binaries

              Other types cannot be added or changed.

              The registry must have been opened in write mode.

       sub_keys(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = {ok, [SubKey]} | {error, ErrorId :: atom()}
                 SubKey = string()

              Returns a list of subkeys  to  the  current  key.  Calls  the  Win32  API  function
              EnumRegKeysEx().

              Avoid calling this on the root keys, as it can be slow.

       value(RegHandle, Name) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Name = name()
                 ReturnValue =
                     {ok, Value :: value()} | {error, ErrorId :: atom()}

              Retrieves  the named value (or default) on the current key. Registry values of type
              REG_SZ are returned as strings. Type REG_DWORD values are returned as integers. All
              other types are returned as binaries.

       values(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = {ok, [ValuePair]} | {error, ErrorId :: atom()}
                 ValuePair = {Name :: name(), Value :: value()}

              Retrieves  a  list  of  all  values  on  the  current  key.  The  values have types
              corresponding to the registry types, see value/2.  Calls  the  Win32  API  function
              EnumRegValuesEx().

SEE ALSO

       erl_posix_msg,  The Windows 95 Registry (book from O'Reilly), Win32 Programmer's Reference
       (from Microsoft)